IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication, in the unlicensed (2.4, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the IEEE 802.11 frequency bands. IEEE 802.11 plays an important role in the growing application of Indoor/Outdoor Location. The key applicable technology is that of ranging using time-of-flight (TOF) ranging measurements defined in IEEE 802.11v. Once the distance between devices is measured, the information can be used to determine device location.
In IEEE 802.11-REVmc, Fine Timing Measurement (FTM) protocol is proposed for Indoor Location. Based on FTM, an initiating station exchanges FTM frames during an FTM session with a responding station to measure the time-of-flight(TOF) or the Round Trip Delay (RTD/2). The initiating station then computes its range to the responding station after receiving timing measurements (i.e., timestamps corresponding to the departure time and arrival time of the FTM frames) from the responding station. To calculate a station position, the station performs ranging measurements with multiple access points (APs) via FTM frame exchange and obtains AP's positions. FTM positioning requires the initiating station to exchange FTM frames with multiple responding APs for TOF measurements in order to determine its absolute location. For 3D positioning, the station needs to exchange FTM frames with four or more APs in order to determine its absolute location.
However, for managed/controlled environments like airports, enterprise, or department stores, it is common to have many Basic Service Sets (BSSs) or Service Set Identifiers (SSIDs) at close locations, i.e. co-located, as shown in FIG. 1. Therefore, it is no benefit for a station (STA) to initiate FTMs with co-located BSSs, because the STA will get the same location and round trip time (RTT). The APs might as well get overloaded with the FTMs. Ideally, STAs would identify co-located BSSs and avoid doing FTM with co-located BSSs. The STA should consider whether co-located BSSs of different capability can provide different level of location information, such as security, accuracy, etc, and whether there are more than one set of location information with respect to the same AP with different accuracy through different BSSs.
One of the conventional method is using multiple BSSID (mBSSID) to signal in beacons which BSSIDs are co-located. The MAC addresses for the co-located BSSs have to be contiguous, otherwise the feature cannot be used. However, the co-located BSSs may be administered by different entities, thus it is not possible to perform coordination between the co-located BSSs.
Another known method is when multiple BSSs are co-located, only one of the BSSs can advertise FTM capability. But this method requires co-ordination between the BSSs. If a STA is associated with one of the BSSs which does not advertise FTM support, it may need to go off the channel to do FTM with the BSS that indicates the support for it. Besides, this method does not allow the BSSs to provide FTM with different resolutions, add-on features, etc. Moreover, if the BSSs belong to different operators, it would be hard to agree which one to advertise FTM support.
Hence, there's a need for a solution for simplified FTM advertising.